An international questionnaire survey aimed at obtaining standardized information to provide insight into many presently unanswered questions as to clinical features of homocystinuria due to cystathionine Beta-synthase deficiency and the effects of various therapies now in use for this condition is underway. Based upon present results and upon projected responses, it appears that by completion of data collection in early 1983 reports will have been obtained upon at least 325 patients, perhaps more. This should be sufficient to provide statistically meaningful answers to the questions raised.